Past, Present and Future States and Variations of the late Quarternary Permafrost Subsystem

Permafrost and seasonally frozen ground comprise a critically important component of the dynamic arctic terrestrial system, constituting a closely tied subsystem interacting with snow cover, vegetation, and the overlying atmosphere. This permafrost subsystem regulates the local exchange of energy, water, and materials (including carbon and nitrogen), and its influence extends beyond the arctic land to the hydrosphere and the extra-tropical climate. Furthermore, the long timescale of permafrost dynamics requires evaluation of the evolution and impacts of the subsystem on the glacial-interglacial time frame. While some recent numerical projections show rapid and widespread degradation of permafrost in response to climate change during this century, global climate system models with physically based snow and permafrost dynamics have not been fully tested, using new observationally-based evidence, for spatial and temporal variability of the subsystem under different climate conditions such as the Holocene optimum or the Last Glacial Maximum (LGM). Evaluation of the climate sensitivity to the permafrost will provide vital insight to future scenarios, especially in the Northern Hemisphere. The focus will be on three late Quaternary eras for which numerical simulations are widely performed by the collaborative efforts of the Paleoclimate Model Intercomparison Project (PMIP: i.e., the preindustrial present (0 ka, where ka = thousand years before present), mid-Holocene (6 ka), and the LGM (21ka). This project will focus on evaluating the structure and function of the permafrost subsystem under different climate conditions.

多年冻土（Permafrost）与季节冻土（seasonally frozen ground）是动态北极陆地系统中至关重要的组成部分，构成了与积雪覆盖、植被及上覆大气紧密耦合的子系统。该冻土子系统调控着局地能量、水分及包括碳、氮在内的物质交换，其影响范围不仅覆盖北极陆地，还延伸至水圈与非热带气候。此外，冻土动力学具有长时间尺度特性，因此需要在冰期-间冰期时间框架下评估该子系统的演化过程及其影响。尽管近期部分数值预测结果显示，本世纪内多年冻土将因气候变化发生快速且大范围的退化，但基于物理过程的积雪与冻土动力学全球气候系统模型，尚未借助新的观测证据完成充分验证——尤其是在全新世适宜期（Holocene optimum）、末次冰盛期（Last Glacial Maximum, LGM）等不同气候背景下，该子系统的时空变异性相关验证仍存在不足。对冻土气候敏感性的评估，将为未来气候情景（尤其是北半球的气候情景）提供关键认知。本项目聚焦晚第四纪的三个时期，这三个时期的数值模拟工作已通过古气候模式比较计划（Paleoclimate Model Intercomparison Project, PMIP）的协同合作得到广泛开展，分别为工业化前基准态（0 ka，其中ka表示距今千年数，即thousand years before present）、中全新世（6 ka）与末次冰盛期（21 ka）。本项目将针对不同气候背景下的冻土子系统结构与功能展开评估。